This invention relates to an audio and video reproduction system having function adjusting an audio reproduction time. The audio and video reproduction system is particularly useful in a multimedia communication system, such as a videophone system, a video conference system, or the like, which uses multiplexed data standardized by an MPEG 2 system standard (ISO/IEC13818-1).
In the multimedia communication system, the audio and video reproduction system receives multiplexed data which comprise video data and audio data incident to the video data. The audio data have a plurality of audio rates which are defined by a plurality of rate modes. The audio and video reproduction system comprises a demultiplexer for demultiplexing the multiplexed data into demultiplexed video data and demultiplexed audio data. The demultiplexed video data are stored into a video buffer memory as stored video data while the demultiplexed audio data are stored into an audio buffer memory as stored audio data. The stored video data are read from the video buffer memory with a video readout rate and are decoded by a video decoder. Similarly, the stored audio data are read from the audio buffer memory with an audio readout rate and are decoded by an audio decoder. The video and the audio decoders are collectively called a decoding block.
In the meantime, the above-mentioned decoding operation must be carried out under a synchronization state of the audio data and the video data. In order to establish the synchronization, it is required to adjust an audio reproduction time, namely, an audio decoding time. Adjustment of the audio reproduction time can be realized by delay adjustment by the use of buffering in the audio buffer memory. In this case, it is required that a mean input rate of the audio buffer memory is equal to a mean output rate of the audio buffer memory. The mean input rate is the rate that the demultiplexed audio data are written into the audio buffer memory. Therefore, the mean input rate is equal to the audio rate. Accordingly, the mean output rate must be equal to the audio rate. This means that the audio rate must be detected before the decoding block in order to adjust the audio reproduction time. However, detection of the audio rate before the decoding block is not yet carried out.